Process for removal of carbonaceous deposits



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found in reciprocating engines. These carbonaceous de- 3i216i357 posits are of such a nature that common carbon removers PROCESS FOR CARBONACEOUS of the organic solvent type will not remove them.

Jacque L. Duvall, West Covina, Calif assignor to Wyan- For proper maintenance of the engines, overhaul pro- 5 cedures must be applied during which the engine compotg g;; wyandom Mich" a cornents are completely and safely cleaned of heat scale or :3 Drawing Filed May 21, 1962, sen 196,468 oxide film deposits, carbonaceous deposits and any other 9 Claims. (CL 134 3) contanunation which may be present. One of the most important reasons for removing the foreign matter and This invention relates to the removal from metal parts N Scale deposits i8 o provide clean metal surfaces which of high temperature deposits, particularly hard carbonare suitable for inspectiomfor flaws by standard techaceous deposits, of the type produced in gas turbine-type q inspection especially important for j engine engines. By the expression deposits of the type produced p s hich are hlghly Stressed, such as nozzle guide in gas turbine-type engines is meant any difiicult to revanes and ue bucketsmove hard carbonaceous deposits formed by the pyrolysis cphvehtlonal Whot of organic materials that are similar in nature to the desectlon components urmg overhaul are based on a composits produced in the hot sections of gas turbine-tym hlnahofi 0f Inadequate h e cleaning methods P engines such as i l j i mechanical cleaning, which includes grit blasting and Gas turbine-type engines are most commonly employed hquld hehlhg vapor h i Thus, r example, at present as turbojet and turboprop power plants for aeohvent'lohalproeedul'e yinclude use ofachlorinated modem i ft and are constructed fro stainksifig} solvent, either hot or cold, followed by a caustic dip, then and other special heat resistant alloys. In general terms, a permanganate treatment, and finally Vapor Sand the jet engine consists basically of two sections: the cold blasting; However, these Procedures P 5 ce ta n insection which consists of the forward part of the engine, hereht elsadvantases- The carbon dePOShS formed d comprising its compressor and other components and the engine operation are hard adherent deposits Which hot section comprising the aft section of the engine which l f heat Scale a which are not removed y comprises the combustion chambers, the turbine wheels eohvehhehal methods using chlorinated Solvent-type and blades, tail cone, combustion chamber shroud, etc. bon removers or hot tank alkaline cleaners. Perman- The stainless steels and other high temperature alloys emgahate, Wheli h a5 a cleaning agent 011 Paris carrying ployed in construction of the hot sections of gas turbinecarbon, preellallates a brown deposit which adds to the type engines are principally those alloys f chromium carbon deposits and heat scale and which makes cleannickel, chromium-nickel-iron, chromium-nickel-cobalt or of the P h more fl flic lt. It is believed that this chromium nickel cobah iron which exhibit adequate 18 due to the reducing action of the residual carbon. As oxidation resistance at the temperatures involved. To be result: the Teslstaht and highly refractory at Scale also classified as a high temperature alloy, it is generally 5 18 hot remPved vfherehy suhseqheht mechanical Cleaning necessary that the meta] be designed to provide high treatment is required which is time consuming, expensive strength as well as oxidation resistance at temperatures of In 9 mammal and manpower d has the effect of 1300 to 1500 F. or higher. The stainless steels are those Wearing away e Surface of the p rt which is detrialloys which likewise exhibit high strength and oxidation mental smce the s lze and Shape Of gas turbine engine-type resistance under high temperature conditions, but genn 13 very cnhcalh' as a sult Of the foreerally do not have as high a strength as the high temperae and Qther deficlehcles, the P Oeedhr e5 frequently ture alloys. fail to provide clean surfaces for inspection since fine In the hot section, temperatures range, on an average, cracks are fined abraslve cold l w of metal which between 400 F. and 1600 F. For example, the turbine may s a crack, thus Preventing detection during an inshaft will generally experience 400 F.; the turbine wheel spectlon cycleitself, 1200 to 1300", and the turbine buckets on the Fmm the abeve dlseusswn, 1t W111 e seen that it is outer extremity of the wheel 16000 or higher in newer necessary to remove the carbonaceous deposits in order engines. The combustion chambers themselves will operto expose the uhderlylhg Oxide heat Scale t0 the action ate at temperatures running almost continually in the of the next treating step such as contacting the parts with 1500 to 16000 R range, with intermittent temperatures an alkaline permanganate solution. Unless the carbonas g as F. aceous deposits are removed before introduction into the At these high operating temperatures, two principal alkalme Pirfhahgahate Solution, the v ry expensive peroccurrences affect the metal components, namely, the l s 15 consumed in the Oxidation of carbon and oxidation of the metals themselves to form what is gen- 1t ls physically blocked from immediate fi live action erally termed a heat scale or oxide film, and the accumulaon metal oxide heat scales thereby etarding such tion of carbonaceous coke-like deposits formed from the actloncombustion of engine fuels. The heat scale is to be distin- In q a e with ac i e, drastic agents guished from ordinary rust produced by c r i f i Such as nitric acid-hydrofluoric acid pickling baths were steel and iron in its physical and chemical nature and is employefl to remove the carbonaceous ePOSitS. One of much more refractory and difllcult to remove. the earhesf a was composed of ferric sulfate and The fuels normally encountered in jet engines are h drofiuonc ta new 0 The p yaliphatic hydrocarbons in nature, very similar to common ment such agents Provides qu te decarbonizing and kerosene. In earlier engines, some aviation gasoline was descahhg but where from the b ck of being highly frequently used containing lead which further complicated cofroslveone 9 the most important and stringent the cleaning procedure. The carbonaceous coke-like dequlremehfs a l engine cleaning Process is a minimum posits which form in gas turbine-type engines as a result of corrosion attack on the y ng metal surface. Due of fuel combustion generally overlay the heat scale, are to the extreme Pfeeisioh nature of most of the P very hard and primarily all carbon with small proportions the corrosion 1055 that is normally considered acceptable of binders of asphaltene, resin, etc. As a result of the in the steel industry cannot be tolerated in j engine high temperatures the deposits are drier, harder, and Overhaul.

higher in carbon content and thus are more difiicult to remove than the conventional carbonaceous deposits Perhaps the most widely used prior art process involves the use of a highly alkaline sggiium hydroxide tn- &

Patented Nov. 9, 1965 ethanola omposition which requires the use of high Tempe 1223:1511 the order of 23s to 300 F. for suitable performance. This composition has certain inherent disadvantages due to excessive expense of the ingredients, coupled with the fact that it operates very slowly. Further, the high temperatures employed and the nature of the solution are hazardous to operating personnel.

Accordingly, it is the purpose of this invention to remove from metal parts, particularly stainm and high temperature alloy parts, high temperature deposits, and particularly hard coke-like carbonaceous deposits, of the type produced in gas turbine-type engines, wherein corrosion of the base metal during treatment is eliminated or substantially reduced and which is economical and may be used in low concentrations at relatively low temperatures.

The method embodying the principles of this invention for removing from metal parts the hard coke-like carbonaceous deposits of the type produced in gas turbinetype engines comprises contacting the parts with an aqueous acidic solution containing ions selected from the group consisting of bi sulfate ions, sulfamate ions and mixtures thereof. The solution may be prepared by dissolving any water-soluble bisulfate compound in water, such as, for example, sodium bisulfate, potassium bisulfate, calcium bisulfate, ammonium bisulfate or sulfamic acid. The solution may also be prepared by dissolving any watersgluble sulfate or sulfamate compound in water, together with the chfiiiically equivalent amount of f to form bisulfate ion or sulfamic acid by chemical reaction in situ, such as, for example, sodium sulfate, potassium sulfate, calcium sulfate, ammonium sulfate and an equal molar amount of sulfuric acid, or sodium sulfamate, potassium sulfamate, calcium sulfamate, ammonium sulfamate and an equal molar amount of sulfuric acid. In general, the solution should have a pH of from to about 2.

This aqueous solution has been found to be effective in almost all proportions, the weaker solutions merely requiring greater treatment times. However, for practical purposes an aqueous solution containing from about 0.15 to 1.00 mol per liter of bisulfate or sulfamate ions or mixtures thereof may be employed although greater or smaller concentration may be employed if desired. A preferred solution contains from about 0.25 to 0.75 mol per liter of bisulfate ions or sulfamate ions or mixtures thereof.

In general, the aqueous solution should be heated and a practical temperature range is from about 140 to 200 F. although higher or lower temperatures may be employed if desired. In general, the metal parts are immersed in a bath of this aqueous solution until the carbonaceous deposit has been removed, after which the metal parts are removed from the solution. In most instances, it is necessary to maintain the parts in the bath for a period of at least about one-half hour. While there is no upper limit to the immersion time, generally the parts-are completely cleaned in about 1% hours and, accordingly, immersion for a greater period of time is unnecessary. Thus, it is preferred to maintain the parts in the bath for a period of about 1% hours and a practical maximum time period is about 4 hours, although immersion for longer periods of time may be employed if desired.

While the. above-described solution is generally satisfactory in most applications, in order to insure minimum corrosiveness it has been found desirable for many applications to include corrosion inhibitors. In general, any well-known corrosion inhibitor effective with sulfuric acid solutions employed for treating steel is satisfactory for this purpose. Examples of such inhibitors are as follows: butyl sulfide, -tol lthiourea, p-tolylthiourea, butyl disulfide, amyl theft imam selenide, propyl sulfide, phenylthiourea, butyl methyl sulfide, diethylthiourea, dibutyl thiourea, butyl mercaptan, p-thiocresol, i-butyl mercaptan, triamyl amine, m-thiocresol, trihexyl amine, ethyl sulfide, valerophenone, 2-thionaphthol, o-thiocresol, propyl mercaptan, methyl sulfide, crotonaldehyde, aldol (Z-OH-butyraldehyde), phenylmorpholine, formaldehyde, ethyl mercaptan, o-tolualdehyde, m-tolualdehyde and p-tolualdehyde. Preferred inhibitors for this purpose are the thioureas. In general, even a very small amount of corrosion inhibitor may be effectively employed. For practical purposes, the minimum amount of inhibitor is about 5X 10" mols per liter of solution. Almost any larger amount of inhibitor may be employed, generally with no detrimental effect other than the expense involved in using greater amounts than necessary. A practical maximum amount of inhibitor would be about 2 l0 mols per liter of the solution although larger amounts may be employed if desired. The use of more than one inhibitor substance may be desirable in many instances.

Since the parts being cleaned frequently have oil or other soils which might interfere with the contact of the solution, it is desirable to incorporate a wetting agent or a plurality of wetting agents in the solution. Any nonionic, anionic, cationic or amphoteric wettingagg may be employed in this solution, with the exception of the soap types which do not retain their wetting properties in acidic solutions.

Exemplary of wetting agents which can be used are (l) alkylarylpolyethers, such as the oxyethylated adducts of nonyl phenol having an oxyethylene content in the range of about 65 to about 85 weight percent of the total molecule and the oxyethylated adducts of tertiary octyl phenol having an exyethylene content in the range of about 65 to about 75 percent by weight of the molecule, and (2) the polyoxyethylene-polyoxypropylenexyethylene (EPE ock p olymer }ipg oi nonionics see U. aten o. 2,674,619,Ii1hdsted), wherein the mo eWghToft e po yoxye nebase is in a range from 800 to about 2500 and the oxyethylene content is from about 30 to about weight percent of the total molecule, which wetting agents are well known in the art. Further examples of wetting agents which can be employed in the compositions of the invention include (3) the well-known u c h a s sodium alkylbenzenesulfonate wherein the alkyl group m a on o 18 car toms, (4) the alkylsulfates such as sodium laurylsulfate, and (5) the ethylene oxide condensation products of primary fatty amines.

The amount of such wetting agent employed may be very small and still be effective and there is no detrimental effect in the use of large amounts other than the undue expense of employing greater amounts than needed. It has been found that an amount of wetting agent as low as 0.01 weight percent of the solution may be employed. A practical maximum amount is 0.5 weight percent of the solution, although larger amounts may be employed if desired. Also, a plurality of wetting agents may be employed.

It has also been found that oxalate ions may be added to the solution with beneficial results in further reduction of corrosion rate and improved cleaning. The oxalate ion may be supplied by adding to the solution any water-soluble oxalate compound such as sodium oxalate, potassium oxalate, calcium oxalate, ammonium oxalate, oxaljp g gig etc. or mixtures thereof. A very small amount of the oxalate ion may be added and it has been found that an amount as small as 5.0x 10* mols per liter of the solution may be employed effectively. In general, any larger amounts may be employed without detrimental effect; however, the desired effectiveness decreases as the amount increases. A practical maximum amount of oxalate ion has been found to 'be about 0.12 mol per liter of the solution.

The above-recited limits in regard to temperature, time, etc. for the aqueous solution containing only bisulfate ion or sulfamic acid are equally applicable to the modified solutions including the additional substances, i.e. inhibitors, Wetting agent and oxalate ions.

An example of a preferred method for removing carbonaceous deposits from jet engine parts comprises contacting the parts at a temperature ranging from about 160 to 180 F. with a composition which consists essentially of, by weight, of dry ingredients 90.1% sodium bisulfate, 5.0% sodium oxalate, 2.4% of an 85% active sodium alkylbenzenesulfonate, 2.0% of 1,3-diethylthiourea and 0.5% of di-o-tolylthiourea dissolved in water to form a 9 to 12 percent by weight aqueous solution of these ingredients. The contact time ranges from about 30 minutes to 2 hours.

The above-described method of treatment is effective for removing undesirable hard coke-like carbonaceous deposits from the above-described types of metal parts and in many instances will completely clean the desired parts. Where it does not completely clean the desired metal parts of heat scale, etc., the remaining deposit may be removed with various other solutions. A particularly effective treatment for removing all high temperature deposits of the type produced in gas turbine'type engines has been found to consist of immersing the parts in the above-described solution of bisulfate ions or sulfamic acid or mixtures thereof for a period of time Sufficient to remove all or a major portion of the undesirable carbonaceous deposits, after which the parts are immersed in an aqueous alkaline permanganate solution. In general, very small amounts or very large amounts of alkaline permanganate solution may be employed, there being no criticality in these limitations, the weaker solutions generally requiring longer periods of time. It has been found that an alkaline permanganate solution containing from about 0.1 to 0.4 mol per liter of permanganate ion and from about 3.0 to 6.0 mols per liter of hydroxyl ion is effective for this purpose although larger or smaller amounts of permanganate and/or hydroxyl ion may be employed if desired. A preferred solution would contain from about 0.15 to 0.25 mol per liter of permanganate ion and from about 4.0 to 5.0 mols per liter of hydroxyl ion. It is preferred to supply the permanganate ion in the form of potassium permanganate or sodium permanganate although any water-soluble permanganate compound may be employed. Any water-soluble alkaline agent containing hydroxyl ions may be employed in such solutions, although-sedinnrandmotassiurn hydroxide are preferred for this purpose.

In general, it is preferred to pressure rinse the parts in water between the two treatments, preferably in warm water, i.e. around 100 F., although heated water is not necessary. The temperature of the potassium permanganate solution is not critical; however a good practical operating range is from about 160 to 220 F. In general, the metal parts are immersed in the permanganate solution for a time period sufiicient to completely clean the parts. At least 60 minutes is generally required to clean the parts and there is no maximum time limit since there is no particular disadvantage to long immersions other than that inherent in employing unnecessary excessive amounts of time. A practical maximum period of time is about 6 hours, although longer time periods may be employed if desired. A preferred treatment for removing all deposits comprises immersing or contacting the parts in the solution of bisulfate ion or sulfamic acid or mixtures thereof for about 1 /2 hours, followed by immersion or contact with the alkaline permanganate solution for about 3 hours.

Another particularly effective treatment for removing all high temperature deposits of the type produced in gas turbine-type engines has been found to consist of immersing the parts in the above-described solutions of bisulfate ions or sulfamic acid, followed by immersing the parts in the above-described alkaline permanganate solution, after which the parts are immersed in an acid pickling bath usually consisting of an aqueous solution of inhibited mineral acids. By the use of this treatment, the time of immersion in the above-described alkaline permanganate solution can be shortened to the time required for a sufficient chemical modification of the heat scale or oxide film, by the oxidizing action of the alkaline permanganate, which thereby renders the heat scale or oxide film acid soluble, rather than continuing treatment with the above-described alkaline permanganate until the parts are completely free of heat scale or oxide film. The over-all processing time may thereby be materially reduced with the subsequent economic advantages. The composition of the acid pickling solution is not critical, any acid solution commonly known in the art to be suitable for pickling metal heat scales being useful. An example of a preferred pickling solution would be a 25% by volume aqueous solution of nitric acid in which the parts are immersed for a period of 15-30 minutes at room temperature. The above-described solutions of bisulfate ions or sulfamic acid or mixtures thereof of this invention may also be employed for the third step in this treatment.

The following examples are provided to illustrate the application of the principles of this invention.

EXAMPLE I A series of fifteen 3-liter aqueous solutions having compositions as indicated in Table 1 below are prepared by dissolving the compounds indicated in Table 1 in water. Each solution is provided in a 7.5 x 6.0 inch diameter open top, stainless steel, cylindrical container or tank and the solution heated to the temperature indicated in Table 1 below and subjected to continuous stirring action by means of laboratory stirring equipment. Fifteen identical groups of jet engine parts coated with hard coke-like carbonaceous deposits and heat scale are immersed in the solutions indicated in Table 1 below for the periods of time indicated. Each group includes a turbine bucket, a combustion chamber interliner section and a turbine nozzle and each group is treated in one of the fifteen solutions as indicated in Table 1 below.

Table 1 Parts Solu- Bisulfate Concentra- Concentra- Weight Concentra- Time Group tion or Sulfamie tion, Oxalate tion, Wetting Percent of Inhibitor tion, T.,F. (Hrs) No. No. Acid Mols/Liter Mols/Liter Agent Solution Mols/Liter 1 1 Sodium 0.50 13 1 bisulfate A 2 do 0.15 Sodium 0.025 Sodium 0.1 Dl-o-tolyl- 2 10- 180 4 oxalate dodecyl thiourea. 9X10- benzene 1,3-diethylsulfonabe thlourea. 3 3 -.-d0 0.50 d0 0.025 -d0 0.1 Di-O-tOlyl- 2Xl0- 180 1% thiourea. 9X10- 1,3-diethy1- thiourea. 4 4 -do 1.00 do 0.025 --d0 0.1 Di-o-tolyl- 2)(10 180 1% thiourea. 9X10 1,3-diethylthiourea. 5 5 Potassium 0.50 do 0.025 .-do 0.1 Di-o-tolyl- 2X10- bisuliate thiourea. 9x10 180 1% 1,3-diethylthiourea.

Table 1Cont.inued Parts Solu- Bisuliate Concentra- Conoentra- Weight Concentra- Time Group tion or Sullamic tion Oxalate tion, Wetting Percent of Inhibitor tion, T., F. (Hrs) No. No. Acid Mols/Liter Mole/Liter Agent Solution Mols/Liter 6 6 Ammonium 0.50 Sodium 0.025 Sodium 0.1 Di-o-tolyl 2X10- 180 1% bisulfate. oxalate. dodecyl thiourea. 9x10 benzene 1,3-diethyl- Sullonate thiourea. 7 7 Calcium 0.50 .--.do 0.025 do 0.1 Di-o-tolyl 2X10- 180 1 bisulfate. thiourea. 9X10- 1,3-diethylthiourea. 8 8 Sulfarme 0.50 do 0.025 do 0.1 Di-o-tolyl 2X10- 180 1% acid. thiourea. 9X10- 1,3-diethylthiourea. 9 9 Sodium 0.50 Oxalic acld 0.025 do 0.1 Di-o-tolyl 2X10 180 1% bisulfate. thiourea. 9 10-= 1,3-diethylthiourea. 10 10 do 0.50 Potassium 0.025 do 0.1 Di-o-toly 2X10- 180 1% oxalate. thiourea. 9X10- 1,3-diethylthiourea. 11 11 -.do 0.50 Sodium 0.025 --do 0.1 Dl-o-tolyl- 2 10- 140 2 oxalate thiourca. 9X10- 1,3-diethylthiourea. 12 12 do 0.50 do 0.025 .do 0.1 Di-o-tolyl- 2X10 200 1% thiourea. 9 10- 1,3-diethy1- thiourea. 13 13 do 1.00 do 0.025 .--do 0.1 Dip-tolyl- 2 10- 180 V thiourea. 9X10- 1,3-diethylthioureu. 14 d0 0.50 ...do 0.025 d0 0.1 Digutyl 5X10 180 1% t iourea. 15 do 0.50 .-.do 0.025 .do 0.1 Phenyl- 5X10-= 180 1% thiourea.

After treatment for the riod of time indicated in Table Pe EXAMPLE III 1, followed by rinsing and drying, all parts are substantially free of the undesirable carbonaceous deposits and in many cases a significant amount of the heat scale is also removed without appreciable corrosion of the parts.

Three 3-liter solutions of bisulfate compounds or sulfamic acid plus other ingredients of this invention are made up having the compositions of solutions Nos. 1, 3 and 8 shown in Table 1 above. These solutions are providcd in containers and stirred, all as described in Example I, and 10 groups of the same three kinds of parts as described in Example I are respectively immersed for 1 hours in solutions of one of these three compositions, as indicated in Table 2 below. These solutions are maintained at a temperature of 180 F. and stirred in the same manner as for the solutions of Example I. Each group of parts is then removed from its respective bisulfate or sulfamic acid solution, pressure rinsed with water at a temperature of 77 F. and immersed in a 3-liter alkaline permanganate solution provided in the same kind of container as that employed for the bisulfate or sulfamic acid solution. tions are indicated in Table 2 below. The permanganate solutions are maintained at the temperatures indicated in Table 2 and immersed for the period of time indicated in Table 2.

The compositions of the permanganate solu- A 3-liter solution having a composition of solution No. 3 of Example I is made up and placed in the type of container described in Example I, heated to and maintained at a temperature of 180 F. and stirred as described in Example I. A group of the same three kinds of parts as described in Example I is immersed in the solution for a period of 1 /2 hours. A 3-liter solution having a composition of alkaline permanganate, solution No. 1 of Table 2, is prepared as described above in Example II and placed in the same kind of container and stirred. After expiration of a 1 /2 hour period of time, the parts are removed from the sodium bisulfate solution, pressure rinsed in water of about 100 F. for two minutes, and immersed in the permanganate solution. The parts are maintained in the permanganate solution for a period of minutes, removed and pressure rinsed as before. The parts are then immersed in a 25% by volume aqueous solution of nitric acid at about 77 F. temperature for a period of 30 minutes, removed, rinsed in water at about F. and dried. After this treatment, the parts are substantially cleaned of all deposits without evidence of appreciable corrosion of the metal.

While there have been shown and described hereinabove Table 2 Bisuliate or Alkaline Permanganate Solution Parts ulfamic 0 Time, Group Acid T., F hrs.

No. Solution Solution M Mols/ OH- Molsl N o. N 0. Liter Liter 1 1 KMnO4-. 0. 20 4. 5 190 3 3 2 KMnO4 0.20 4.5 190 3 8 3 M11104--." 0.20 4. 5 190 3 3 4 KMnO4 0. 10 4. 5 190 3 3 5 KMnO4. 0. 40 4. 5 190 3 3 6 KMnOi 0.20 4. 5 190 3 3 7 KMnO4 0. 20 4. 5 3 3 8 KMJ1O4 0. 20 4. 5 220 3 3 9 KMn04- 0.20 6.0 220 1 3 10 NaMuO4.. 0. 20 4. 5 3

After treatment in the permanganate solution for the time period indicated in Table 2, followed by pressure rinsing with water at 77 F., all parts are substantially cleaned of all deposits without evidence of appreciable corrosion.

the preferred embodiments of this invention, it is to be understood that various changes, alterations and modifications can be made thereto without departing from the spirit and scope thereof as defined in the appended claims.

I claim:

1. The method of removing from metal parts carbonaceous deposits of the type produced in gas turbine-type engines comprising immersing said parts for a period of from about 30 minutes to 2 hours at a temperature ranging from about 160 to 180 F. in a composition consisting essentially of, by weight of dry ingredients, 90.1% sodium hisulfate, 5.0% sodium oxalate, 2.4% of an 85% active sodium alkylbenzenesulfonate wherein the alkyl group has from about 10 to 18 carbon atoms, 2.0% of 1,3-diethylthiourea and 0.5% of di-o-tolylthiourea dissolved in water to form a 9-12% by weight aqueous solution of said dry ingredients, balance water.

2. A method of removing from metal parts carbonaceous deposits of the type produced in gas turbine-type engines comprising immersing said parts in an aqueous solution selected from the group consisting of sodium bisulfate, potassium bisulfate, calcium bisulfate and ammonium bisulfate, aqueous solutions wherein at least about 0.15 mole per liter of bisulfate ions are present in the solution.

3. The method of claim 2 wherein about 0.15 to 1.0 moles per liter of bisulfate ions are present in the solution.

4. The method of claim 2 wherein about 0.25 to 0.75 moles per liter of hisulfate ions are present in the solution.

5. The method of claim 2 wherein said aqueous solution has a pH of from to about 2.

6. A method of removing from metal parts carbonaceous deposits of the type produced in gas turbine-type engines comprising immersing said parts in an aqueous sodium bisulfate solution wherein at least about 0.15 mole per liter of bisulfate ions are present in the solution.

7. A method of removing from metal parts carbonaceous deposits of the type produced in gas turbine-type engines comprising immersing said parts in an aqueous potassium bisulfate solution wherein at least about 0.15 mole per liter of bisulfate ions are present in the solution.

8. A method of removing from metal parts carbonaceous deposits of the type produced in gas turbine-type engines comprising immersing said parts in an aqueous calcium bisulfate solution wherein at least about 0.15 mole per liter of bisulfate ions are present in the solution.

9. A method of removing from metal parts carbonaceous deposits of the type produced in gas turbine-type engines comprising immersing said parts in an aqueous ammonium bisulfate solution wherein at least about 0.15 mole per liter of bisulfate ions are present in the solution.

References Cited by the Examiner UNITED STATES PATENTS 1,852,648 4/32 Gravell 252-l49 XR 2,220,451 1=1/40 Hunt 252-l42 2,287,050 6/42 Miller 252-l42 2,316,220 4/43 Brown et a1. 252-142 2,408,424 10/46 Healy et al. 252-142 2,643,205 6/53 Murray 13428 3,033,795 5/62 Brevik 252l42 3,074,824 1/63 Binger 13428 3,114,657 12/63 Stilwell 252-149 XR FOREIGN PATENTS 532,661 l/4l Great Britain.

JULIUS GREENWALD, Primary Examiner. 

1. THE METHOD OF REMOVING FROM METAL PARTS CARBONACEOUS DEPOSITS OF THE TYPE PRODUCED IN GAS TURBINE-TYPE ENGINES COMPRISING IMMERSING SAID PARTS FOR A PERIOD OF FROM ABOUT 30 MINUTES TO 2 HOURS AT A TEMPERATURE RANGING FROM ABOUT 160* TO 180*F. IN A COMPOSITION CONSISTING ESSENTIALLY OF, BY WEIGHT OF DRY INGREDIENTS, 90.1% SODIUM BISULFATE, 5.0% SODIUM OXALATE, 2.4% OF AN 85% ACTIVE SODIUM ALKYLBENZENESULFONATE WHEREIN THE ALKYL GROUP HAS FROM ABOUT 10 TO 18 CARBON ATOMS, 2.0% OF 1,3-DIETHYLTHIOUREA AND 0.5% OF DI-O-TOLYLTHIOUREA DISSOLVED IN WATER TO FORM A 9-12% BY WEIGHT AQUEOUS SOLUTION OF SAID DRY INGREDIENTS, BALANCE WATER. 